The kingdom extended measures to combat the spread of the coronavirus, which has infected more than 1,700 people and killed 16.
Saudi’s Interior Ministry said in a statement that there were some exceptions for essential workers and for residents to buy food and access medical care.
Cars in those cities’ residential districts may only carry one passenger to limit the virus’ transmission, it said.
The country of 30 million has taken drastic steps to contain the disease, halting international flights, closing most public places and suspending the year-round Umrah Pilgrimage.
On Tuesday, it asked Muslims to put plans for the annual hajj pilgrimage on hold pending more clarity about the pandemic.
Restrictions on movement have tightened, with entry and exit to Riyadh, Mecca, Medina and Jeddah heavily restricted.
Some neighbourhoods in Mecca and Medina were already under full lockdown, but in the rest of those cities, the curfew was previously from 1500 to 0600.
The eastern oil-producing province of Qatif, where the kingdom’s first coronavirus cases were reported last month among Shi’ite Muslim pilgrims returning from Iran, has been on lockdown for nearly four weeks.
Saudi Arabia has the most infections and deaths among the six-member Gulf Cooperation Council.